Lexicon 20 BIT A-D CONVERTER REV 0, 20, 20 AD User Manual

20/20 AD

20 Bit A/D Converter

User Guide

Lexicon

Precautions

The 20/20 AD is a rugged device with extensive electronic protection. However, you should observe the same reasonable precautions that apply to any piece of audio equipment:

• Always use the correct line voltage.

• Do not install the 20/20 AD in a closed, unventilated rack, or directly above heat-producing equipment such as power amplifiers.

• Never attach audio power amplifier outputs (speaker outputs) directly to any of the 20/20 AD's connectors.

• To prevent fire or shock hazard, do not expose the 20/20 AD to rain or moisture.

Notice

This equipment generates and uses radio frequency energy and if not installed and used properly, that is, in strict accordance with the manufacturer's instructions, may cause interference to radio and television reception. It has been type tested and found to comply with the limits for a Class A computing device in accordance with the specifications in Subpart J of Part 15 of FCC Rules, which are designated to provide reasonable protection against such interference in a residential installation. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause interference to radio or television reception, which can be determined by turning the equipment OFF and ON, the user is encouraged to try to correct the interference by one or more of the following measures:

Reorient the receiving antenna Relocate the computer with respect to the receiver Move the computer away from the receiver Plug the computer into a different outlet so that the computer and receiver are on different branch circuits.

If necessary, the user should consult the dealer or an experienced radio/television technician for additional suggestions. The user may find the following booklet prepared by the Federal Communications Commission helpful:

"How to identify and Resolve Radio/TV Interference Problems."

This booklet is available from the U.S. Government Printing Office, Washington, DC 20402, Stock No. 004-00000345-4.

This triangle, which appears on your component, alerts you to the presence of uninsulated, dangerous voltage inside the enclosure...voltage that may be sufficient to constitute a risk of shock.

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

This triangle, which appears on your component, alerts you to important operating and maintenance instructions in this accompanying literature.

3 Oak Park Bedford, MA 01730 USA Tel 781-280-0300

by any means or in any form, without express prior consent in writing from Lexicon.

Lexicon Part # 070-09090 Rev 1

Printed in the United States of America

20/20 AD User Guide

SAFETY SUMMARY

The following general safety precautions must be observed during all phases of operation, service and repair of this instrument. Failure to comply with these precautions, or with specific warnings elsewhere in these instructions violates safety standards of design manufacture and intended use of the instrument. Lexicon assumes no liability for the customer's failure to comply with these requirements.

GROUND THE INSTRUMENT

To minimize shock hazard the instrument chassis and cabinet must be connected to an electrical ground. The instrument is equipped with a three-conductor AC power cable. The power cable must either be plugged into an approved three-contact electrical outlet or used with a three-contact to two-contact adapter with the grounding wire (green) firmly connected to an electrical ground (safety ground) at the power outlet. The power jack and mating plug of the power cable meet International Electrotechnical Commission (IEC) safety standards.

DO NOT OPERATE IN AN EXPLOSIVE

ATMOSPHERE

Do not operate the instrument in the presence of flammable gases or fumes. Operation of any electrical instrument in such an environment constitutes a definite safety hazard.

KEEP AWAY FROM LIVE CIRCUITS

Operating personnel must not remove instrument covers. Component replacement and internal adjustments must be made by qualified maintenance personnel. Do not replace components with power cable connected. Under certain conditions, dangerous voltages may exist even with the power cable removed. To avoid injuries, always disconnect power and discharge circuits before touching them.

DO NOT SERVICE OR ADJUST ALONE

Do not attempt internal service or adjustment unless another person, capable of rendering first aid and resuscitation, is present.

General definitions of safety symbols used on equipment or in manuals.

Instruction manual symbol: the product will be marked with this symbol when it is necessary for the user to refer to the instruction manual in order to protect against damage to the instrument.

Indicates dangerous voltage. (Terminals fed from the interior by voltage exceeding 1000 volts must be so marked.)

The WARNING sign denotes a hazard. It

WARNING

CAUTION

NOTE:

calls attention to a procedure, practice, condition or the like which, if not correctly performed or adhered to, could result in injury or death to personnel.

The CAUTION sign denotes a hazard. It calls attention to an operating procedure, practice, condition or the like which, if not correctly performed or adhered to, could result in damage to or destruction of part or all of the product.

The NOTE sign denotes important information. It calls attention to procedure, practice, condition or the like which is essential to highlight.

DO NOT SUBSTITUTE PARTS OR MODIFY

INSTRUMENT

Because of the danger of introducing additional hazards, do not install substitute parts or perform any unauthorized modification to the instrument.

DANGEROUS PROCEDURE WARNINGS

Warnings, such as the example below, precede potentially dangerous procedures throughout this manual. Instructions contained in the warnings must be followed.

WARNING

Dangerous voltages, capable of causing death, are present in this instrument. Use extreme caution when handling, testing and adjusting.

SAFETY SYMBOLS

CAUTION

Electrostatic Discharge (ESD) Precautions

The following practices minimize possible damage to ICs resulting from electrostatic discharge or improper insertion.

• Keep parts in original containers until ready for use.

• Avoid having plastic, vinyl or styrofoam in the work area.

•. Wear an anti-static wrist-strap.

• Discharge personal static before handling devices.

• Remove and insert boards with care.

• When removing boards, handle only by non-conductive surfaces and never touch open-edge connectors except at a static-free workstation.*

• Minimize handling of ICs.

•. Handle each IC by its body.

• Do not slide ICs or boards over any surface.

• Insert ICs with the proper orientation, and watch for bent pins on ICs.

• Use anti-static containers for handling and transport.

*To make a plastic-laminated workbench anti-static, wash with a solution of Lux liquid detergent, and allow to dry without rinsing.

20/20 AD User Guide

Introduction

Controls and Connectors ......................................................................1

Unpacking • Power • Mounting ..........................................................1

Front Panel Controls..........................................................................2

The Converter • The Level Meters • The Compressor

Synchronization and Output Formatting • Alternate Modes

Rear Panel Connectors ..................................................................... 5

Audio Connections ............................................................................6

Connectors • Cables

Using the 20/20 AD.................................................................................9

Analog Inputs.....................................................................................9

Termination and Grounding via Internal Jumpers .............................9

Balanced and Unbalanced Input Signals.........................................12

Front Panel Adjustments .................................................................13

Synchronization and Sample Rate ..................................................14

AES Sync • Word Clock • Internal and External Modes

About Dither.....................................................................................16

Psychoacoustically Optimized Noise Shaping (PONS)

Automatic Offset Removal...............................................................18

Compressor Modes .........................................................................18

Dynamic Range Compression • Non-Linear Transfer

Functions • Overload Protection • Digitizing Analog Tape

Link • Display

Digital Audio Outputs.......................................................................23

Realigning Two DAT Recordings ....................................................24

Digital Sinewave Generator.............................................................24

Contents

Specifications.......................................................................................25

Definition of Terms ..............................................................................27

20/20 AD User Guide

The 20/20 AD is an analog-to-digital converter which can be configured for two 20-bit channels, or four 18-bit channels. Twin on-board signal processors provide 20-bit to 16-bit compression in the digital domain, as well as DC removal and a choice of four dither types.

The compressor allows leeway in setting levels and provides insurance against clipping in the digital domain. In addition, it provides 195 soft

compression curves and 13 time constants to allow for more creative functions, such as emulation of tape saturation or analog compression.

This manual provides some basic information on conversion, but assumes the user will be familiar with the principles of analog-to-digital conversion, as well as with the digital audio interface formats output by the 20/20 AD.

Information on specific data which may be required by any target device should be obtained from the manufacturer.

Introduction

Lexicon has attempted to provide correct information and functional capability corresponding to digital audio standards known and available to us at the time of publication of this document and manufacture of this instrument. As standards evolve, Lexicon may make updates to documentation and/or system software available for purchase.

Lexicon's warranty on this product excludes consequential damages resulting from the use of this product. Local jurisdiction may extend the user additional rights.

AES/EBU Interface (Professional)

The AES/EBU interface conforms to both the AES3-1992 (ANSI S4.40-1992) specification and the EBU document, Tech 3250-E. Both inputs and outputs are balanced, transformer-coupled designs, with a female XLR input and a male XLR output, conforming to the standard convention of IEC 268, Part 12. Input and output levels comply with CCITT V.11. On this device, the professional form of the digital audio and auxiliary data has been labeled "AES" in accordance with general usage.

S/PDIF – Sony/Phillips Digital Interface Format (Consumer)

The S/PDIF interface conforms to the Channel Status Type II format, as specified in the EIAJ CP-340 Digtial Audio Interface Standard, dated September, 1987, and to IEC 958, First Edition 1989-03. As of November 20, 1991, amendments to IEC 958, which include specifications for the implementation of auxiliary data for the consumer format, were under review. Until new specifications are published, this device must conform to currently approved specifications. On this device, the consumer form of the digital audio and auxiliary data has been labeled "SPDIF" in accordance with general usage.

20/20 AD User Guide

Controls and

Controls and Connectors

Connectors

After unpacking the 20/20 AD, save all packing materials in case you ever need to ship the unit. Thoroughly inspect the 20/20 AD and packing materials for signs of damage. Report any shipment damage to the carrier at once. The following accessories are included with the 20/20 AD:

1. Power Cable

2. User Guide

3. Quick Reference Guide

The 20/20 AD is equipped with a 3-pin IEC connector and detachable line cord. Connect the cable end of the 20/20 AD line cord to the 20/20 AD power connector. Then plug the line cord into an AC wall socket providing voltage corresponding to the data plate on the unit.

The 20/20 AD measures 19"W x 1.75"H x 13.9"D (483 x 45 x 353 mm). Make sure that the 20/20 AD is securely screwed into the rack, and that support is provided for the rear of the chassis during transport to avoid possible damage from severe mechanical shock.

Unpacking

Power

Mounting

The maximum ambient operating temperature is 95°F (35°C). Provide adequate ventilation if the 20/20 AD is mounted in a closed rack with heat-producing equipment.

Controls and Connectors

20/20 AD

Front Panel

Controls





THRESHUNBAL THRESHUNBAL

OVL

0 3 6 12 18 24 30 36 42 60

The 20/20 AD front panel controls are divided into three functional groups for conversion, compression, and synchronization/output formatting.

Converter Compressor





1dB SCALE

ALT

PK HOLD

ATTEN

MUTE

2 3



THRESHUNBAL THRESHUNBAL



OVL

0 3 6 12 18 24 30 36

•

–





4 CHAN

EMPH



RMT

VID



DISPLAY

LINK







DIGITAL COMP/LIMITER

GAIN



100 mS

-14

-18

-10

-22

-6

-26

THRESHOLD RELEASE

+•–

0-36

Synchronization and

Output Formatting



1S10

∞



DITHER

FORMAT

AES / WC:



WIDE

HF 48

AES

PRES





20BIT PL DN

SAMPLE RATE

44.1

SPDIF

EXT SYNC

AES

LOCK

Lexicon



POWER

20/20 AD

20 BIT A/D CONVERTER

The Converter

THRESHUNBAL THRESHUNBAL

1dB SCALE

Press to select 1dB Scale display on level meters.

Also used to select alternate modes.

OVL

0 3

6 12 18 24 30 36 42 60

Gain Controls: 1, 2, 3 and 4

Provide continuously variable gain control over a 30dB range.

Note: In 2-channel mode, only 1 and 2 are active.

1dB SCALE

ALT

PK HOLD

ATTEN

MUTE

2 3

THRESHUNBAL THRESHUNBAL

M C P

PK HOLD

Press to cause the level meter LEDs to hold at the highest level received. Press again to deactivate.

UNBAL

Lights when there is a mismatch between the input signal and the setting of the rear-panel Balance switch.*

OVL

0 3

6 12 18 24 30 36

•

–

4 CHAN

EMPH

ATTEN

Press to attenuate balanced input signals by 6dB. Press again to turn attenuation off. Do not use this control on unbalanced signals.

THRESH

When the compressor is on, indicates that the input level has risen above the selected compression threshold.

4 CHAN

Push on-push off selection of 2-channel or 4-channel mode; lit when in 4-channel mode.

EMPH

Turns pre-emphasis on and off.

* Non-linearity of the potentiometer can cause the signal to become unbalanced when the level knob is set to 11:30. To correct this, turn the knob slightly in either direction until the UNBAL light goes out.

20/20 AD User Guide

1dB SCALE

GAIN

REDUCTION

NORMAL

OVL

-1

-2

-3

-4

-5

-6

-7

-8

-9

1 2 3 4 5 6 7 8

9 10 11

OVL

-3

-6

-12

-18

-24

-30

-36

-42

-60

- red -

- yellow -

- green -

OVL

0 3

6 12 18 24 30 36 42 60

Controls and Connectors

The Level Meters

When the compressor is

off

, the behavior of the level meters is determined by the settings

of the 1dB SCALE, and PK HOLD switches. When the compressor is

, pressing DISPLAY will cause

gain reduction (in dB)

to be

displayed on the two right hand meters (2-channel mode) or on all four meters (4-channel mode).

The following charts show all of the possible states of the level meter and the value in decibels for each state.

Switches ON Meters 1 & 2 Meters 3 & 4

4-Channel

Mode

2-Channel

Mode

none

1 dB SCALE

DISPLAY

none

1 dB SCALE

DISPLAY

Normal

1 dB Scale

Gain Reduction

Normal Normal Normal

Normal

1 dB Scale

Gain Reduction

(Blank)

1 dB Scale

Gain Reduction

DISPLAY

Press to cause gain reduction to be displayed on the level meters — In 2-channel mode, only the right two level meters are activated; in 4channel mode, all four level meters display compression. Press again to deactivate.

LINK

In 2-channel mode, links the left and right compressors ; in 4-channel mode, where 1,2 and 3,4 are already linked, this control links the two pairs.

Turns the compressor on and off.

DISPLAY

RMT

VID

LINK

GAIN

Adjusts the gain of low level signals (below the compression threshold) between the converter and the compressor.

DIGITAL COMP/LIMITER

-14

-18

-22

-26 0-36

THRESHOLD RELEASE

THRESHOLD

Sets the level at which compression starts.

The Compressor

100

-10

-6

∞

–+

•

RELEASE

This control allows adjustment of the release time of the compressor. Release times from 0mS to ∞ are available. The attack time of the compressor is automatically set as a function of the signal rise time.

Controls and Connectors

Synchronization

Output Formatting

Lexicon

and

DITHER

Selects the type of dither: wide bandwidth, 20 bit, or High Frequency .

FORMAT

Selects the format to be available at the output connectors, AES or S/PDIF.

Note: The format selected

all

here will be sent to puts.

out-

Alternate Modes

DITHER

FORMAT

AES / WC:

AES/WC

In internal sync mode, PRES indicates that AES is available at the inputs as a sync source.

In external sync mode, PRES indicates that the sync source is present at the input connectors.

either

WIDE

AES

PRES

selected

20 BIT PL DN

SAMPLE RATE

44.1

SPDIF

AES

LOCK

EXT SYNC

LOCK lights in external sync mode to indicate the unit has successfully locked to the incoming signal (WC or AES).

SAMPLE RATE

Selects the sample rate of the A/D conversion. This switch should be set to the same sample rate as your sync source. When Word Clock is selected as an external sync source, the AES Channel Status Sample Rate bit will be set to the sample rate value you have selected here.

(The PL DN setting of this switch is reserved for future enhancements.)

EXT SYNC

This switch allows selection of: Internal mode (unlit), Word Clock source, or AES source.

ALT - ATTEN

Mutes the outputs. Note that the level meters still work. To unmute, hold ALT and press ATTEN again.

ALT - 4 CHAN

Activates output of a digital sinewave at the AES ports.

To activate the alternate modes...

press and hold ...then press one of these.





1dB SCALE

ALT







MUTE



ATTEN

4 CHAN







DISPLAY

RMT



LINK



Repeat to exit the alternate mode.

ALT - DISPLAY

Activates remote mode/front panel lockout. When activated, the 1dB SCALE and DISPLAY LEDs flash and front panel controls are locked into their current settings. To unlock, hold ALT and press DISPLAY again.

VID

ALT - LINK

Only active in 4-channel mode. Activates a short tone burst. See

DAT Recordings.

ALT - ON

Reserved for future enhancements.

Realigning Two





DITHER

ALT - DITHER

Activates psychoacoustically optimized noise shaping. When activated, WIDE, 20BIT and HF will be lighted.

Note that this type of dither can only be used in 2-channel mode; activating will disable 4-channel mode and compressor functions.

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